Starting circuit for arc lamp



Sept. 6, 1960 H. E. SCHULTZ 2,951,971

STARTING CIRCUIT FOR ARC LAMP Filed may 2, 1957 Fig}. nf IB F23. 1 12. 2. T5

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United States STARTING CIRCUIT FOR ARC LAMP Harry E. Schultz, Euclid, Ohio, assignor to General Electric Company, a corporation of New York This invention relates in general to a circuit for providing starting pulses of high voltage to an arc lamp in con junction with a pulsed waveform operating circuit. Such a pulse-generating circuit may be used to effect the initial ionization of the discharge medium in the lamp, particularly where the breakdown voltage is of the order of several times the normal operating-voltage of the lamp.

The invention is particularly useful with are lamps of the kind frequently referred to as fiashtubes, requiring a high instantaneous loading in order to have a high light output. When the instantaneous loading is high, the spectrum of the radiation produced contains, in addition to the usual line spectrum of the inert rare gas filling such as xenon, a continuum of radiation of substantial intensity whose over-all color is close to that of natural daylight. In flashtubeor stroboscopic applications, the common method of energization of these lamps has been to I charge a capacitor to a relatively high voltage, usually several hundred volts, which is then discharged through the flashtube connected across it. The discharge through the flashtube is initiated by applying a pulse to a triggering electrode which may take the form of a .capacitive element disposed along the lamp, for instance a wire spiralled around the flashtube.

Where continuous pulsed operation of an'arc lamp or flashtube is desired, the capacitor discharge method of operation has several limitations. In the first place it is basically inefficient by virtue of the losses in the system for charging the capacitor. In the second place, the residual ionization remaining in the lamp limits the rate of flashing or the loading below the levelat which continuous conduction through the lamp prevents the buildupof charge in the capacitor.

In copending application Serial No. 656,595 of Emmett H. Wiley, filed of even date herewith, entitled Pulse Circuit for Arc Lamp, and assigned to the same assignee as the present invention, there is described and claimed an alternating current pulsed operating circuit. This circuit uses a saturable reactor to provide high-intensity short duration current pulses for energizing an arc lamp or flashtube with high instantaneous loading and wherein the magnetizing current of the reactor is used to maintain ionization within the lamp between pulses. For economical design, the circuit must provide high-current pulses at a relatively low voltage generally insufiicient to start the lamp though sufficient to repeat the pulsed discharge at cyclic intervals after initial ionization has been produced. It is therefore necessary to provide some means to effect initial ionization of the lamp for starting purposes.

The object of the invention is to provide a new and improved circuit for generating high-voltage starting pulses to effect the initial ionization of an arc lamp.

A more specific object of the invention is to provide a circuit combination which will generate high voltage and relatively low current pulses for starting a discharge within an arc lamp, and high current relatively low-voltage pulses for energizing the arc lamp with high instantaneous loading after initial j'ionization has been efiected.

' atent Patented Sept. 6, race ice a rectangular hysteresis loop characteristic. This inductor is connected, in series with a coupling winding on the saturable inductor of the main loop, across a capacitor charged from an alternating voltage source through a current limiting impedance. The capacitor discharges through the saturable inductor at the instant when saturation is reached and its incremental inductance falls substantially to zero. A high-current pulse thus occurs through the coupling winding which generates a high voltage pulse in the saturable inductor of the current regulating loop and thereby ionizes the arc lamp.

In a preferred embodiment, both the main discharge current regulating loop and the auxiliary starting loop use a saturable inductor having a high-permeability core with substantially rectangular hysteresis loop characteristic. The circuit of both the main loop and the auxiliary loop are similar, there being provided in each loop a T-network consisting of a current limiting inductor and a capacitor connected across an alternating voltage source. In the main loop, the saturable reactor is connected in series with the arc lamp acrossthe capacitor. In the auxiliary loop, the saturable reactor is connected, in series with the coupling winding on the saturable reactor of the main loop, across the capacitor. At starting, the auxiliary loop produces high-current pulses through the coupling winding which induces high-voltage pulses in the saturable reactor of the main loop for ionizing the arc lamp. After the lamp has started, the saturable reactor of the main loop provides high-current pulses through the arc lamp resulting in the desired high instantaneous loading.

For further objects and advantages and for a detailed description of a preferred embodiment of the invention and its mode of operation, attention is now directed to the following description and accompanying drawing. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

Fig. 1 illustrates diagrammatically an elongated arc lamp or flashtube with an operating circuit therefor embodying the invention.

Fig. 2 illustrates the rectangular hysteresis loop characteristic of the core material of the saturable reactors used in the circuit of Fig. 1.

Fig. 3 shows current and voltage wave forms in the circuit of Fig. 1.

Fig. 4 is a schematic diagram of a modified circuit embodying the invention.

Referring to the drawing and more particularly to Fig. 1, the circuit illustrated is designed for the operation of an arc lamp or flashtube F consisting of an elongated tubular quartz envelope 1 provide with activated thermionic self-heating electrodes 2 at opposite ends. Each elec trode may consist of a tungsten wire helix 3 wound about the inwardly projecting end of the inlead and a thorium sliver disposed alongside. The inleads include foil portions 4 of molybdenum pinch-sealed through the end of the tube. The tube is filled with an inert gas such as xenon at a pressure below atmospheric pressure. As an example, are lamp F may consist of a quartz tube 11" in over-all length, A" in diameter, and with a xenon fillconsist of similar reactive elements forming T-networks.

The auxiliary loop is connected across input terminals T T adapted to be energized from a volt, cycle ass gn.

supply. Closing switch S connects reactor L and capacitor C in series across the voltage supply. L is a substantially linear reactor and is shown as a winding 6 about the central leg of an E lamination 7 provided with an air gap at 8 next the end lamination 9 to prevent saturation of the core, A saturable reactor L is connected across C in series with a coupling winding L wound about the core of a similar saturating reactor L; of the main current regulating loop.

In the main loop, closing switch S connects reactor L and capacitor C in series across input terminals T T adapted to be connected to a 280 volt, 60 cycle supply. Reactor L like reactor L is substantially linear in characteristics and is shown as a winding 10 on the central leg of an E lamination 11 provided with the usual air gap at 1.2 next the end lamination 13.

Saturable reactor L is connected in series with the lamp F across capacitor C being for that purpose connected between one side of capacitor C and output terminal T while the other side of C is connected directly to output terminal T Both'saturating reactors L and L; are wound about toroidal cores 14 and 15 respectively, consisting of grain oriented silicon steel or nickel-iron strip continuously wound in the usual fashion to preserve the grain orientation parallel to the direction to magnetization. The magnetic core material is, of a high-permeability, high-saturation flux density type having a rectangular hysteresis loop characteristic. Such a characteristic is illustrated in Fig. 2 showing the flux density B increasing very rapidly with the magnetizing force H up to the saturation levels S beyond which there is almost no further increase in flux density. Below saturation, the incremental permeability is given by the slope of dotted line 16, whereas beyond saturation the incremental permeability is substantially that in air and equal to 1. The ratio of incremental permeabilities below and above saturation may be in the range of 10,000 to 1. Grain oriented silicon steel may be used for core 15 of L and nickel iron having a yet smaller and more rectangular hysteresis loop is preferably used for core 14 of L ickel iron core material of this type is sold under the various trade names Deltamax, Orthonol, and Permeron.

In the operation of the auxiliary starting circuit, when switch S is closed, capacitor C charges through linear reactor L until its voltage is suflicient to saturate saturable reactor L The charging voltage wave form is shown by curve 21 of Fig. 3a; the charging occurs in a generally positive direction from time t to 1 and in a generally negative direction from t to t At the voltage level corresponding to t saturable reactor L saturates. At this instant, its incremental permeability may drop by a factor of 10,000 and its inductive reactance falls through the same ratio. Accordingly, capacitor C discharges rapidly through the saturable reactor providing the current pulse shown by curve 22 at time t in Fig. 3b. This current pulse passes through winding L on saturable reactor L and the resulting rapid change in flux in the core induces a high-voltage pulse in main winding L shown by curve 23 at time t in Fig. 3c. A half cycle later at time t the capacitor discharges in the opposite direction and produces the current pulse shown by curve 22 and the corresponding voltage pulse shown by curve 23. The interval from t to t or t to t corresponds to /2 cycle of the supply voltage shown by dotted line curve 24, namely second. The sequence of high voltage pulses applied across the arc lamp causes the xenon filling therein to become ionized.

Switch S of the main current regulating loop may be closed at the same time as switch S of the auxiliary starting loop, or at any time thereafter, in order'to place the lamp F in normal operation. The main loop operates in 4 .v the same fashion as the auxiliary loop as regards the generation of the current pulses. However, its current pulses are used to energize the lamp directly rather than to provide high voltage pulses for the initial ionization. Capacitor C charges through linear reactor L until the voltage across it is sufiicient to saturate the core of saturable reactor L At this instant, the inductance of saturable reactor L drops approximately in the ratio of incremental penneabilities of the core below'and' above saturation. This allows the charge. across capacitor C to be discharged in a short high-intensity pulse through the lamp. The discharge current wave form through the lamp is illustrated by curve 25 in Fig. 3'di The current pulses occur at times t and r twice per'cycle, that is with a time interval of second apart. Times i and A; may or may not correspond to times t and t depending upon the adjustment of the circuit elements.

' If the. Voltage-time. integral of the charge across capacitor Ci reaches the saturation level of. saturable reactor L early in the half-cycle of the supply frequency, the capacitor may recharge to the saturation level in time to generate one ofmore; additional pulses within the halfcycle, as shown by dotted pulses 22', 22 trailing main pulses 22 in Fig. 3b. This may be made use of in the auxiliary starting circuit to increase the speed with which the lamp is ionized. In the main discharge regulating loop, the voltage-time integral of charge across capacitor C may. likewise reach the saturation level of saturable reactor L more than once during each half-cycle of the supply voltage.

The design criteria governing the choice of constants for the various circuit elements and the values selected for a unit actually constructed. and found to operate under test as previously described areas fiollows.

The size of capacitor C determines the loading or watt input into the lamp, and the voltage applied to terminals T T must be sufficient to cause the discharge through the lamp to take place. If the applied voltage is too low, the discharge willv not occur whereas if it is too high, unstable operation with multiple discharges and oscillations per half-cycle will occur as previously explained. For a loading of 1250 watts into the lamp previously described, a voltage supply of 280 volts with a value for C501? 42 microfarads is appropriate. Linear inductance L must allow the recharging of capacitor C to the operating, value so that the voltage-time integral allows the build up of sufificient flux to exceed the saturation level of; saturable reactor L at each half-cycle. The value selected for L is .04 henry and is achieved by approximately 165 turns on a core cross section 2" x 1 /2" measured at the winding leg of E lamination 11. The saturating reactor L is chosen to saturate once per half cycle at a voltage on the charging cycle above the maintaining voltage required for are lamp F. In other words, the saturating reactor must have sufiicient turns coupled with a cross sectional area achieving saturation on the charging cycle at or slightly above the striking voltage of the lamp. The saturable reactor used consists of turns on a toroidal core of grain-oriented silicon steel 1%" x 1% in cross section, 3 inner diameter and 6 /2 outer diameter.

In the auxiliary starting loop, the value capacitor C determines the energy transferred 'into the main current regulating circuit in the form of high-voltage ionizing pulses;' The linear reactor'L is proportioned to allow capacitor Cito charge to the saturating level'of saturable inductor L at least once per half cycle. In the unit con toroidal core of'high-perm e'ability nickel-iron Deltamax strip with a rectangular hysteresis loop characteristic,

/2 x 1" in cross section, 2 /2" inner diameter and 3 /2 outer diameter. Coupling winding L consists of sufficient turns on the core of saturable reactor L to obtain eflicient transfer of energy along with substantial voltage multiplication. In the unit constructed, L consists of 5 turns on core 13 of saturable inductor L,,; the winding ratio as between L, and L is 160 to 5, providing a voltage multiplication of 32. i V a The circuit which has been described starts the illustrated lamp with pulses of approximately 3,000 volt peak amplitude at @5 second time interval repetition, that is at 8,333 microsecond intervals. During normal operation, the arc lamp operates witha current pulse of approximately 77 amperes peak current and approximately 500 microsecond pulse width at percent of maximum amplitude, the time interval between pulses being 8,333 microsecond, that is a repetitionrate of 120 per second. The eifective or R.M.S. value of current into the lamp is 13.6 amperes at a voltage drop of 117.5 volt and-the energy input into the lamp is 1260 watts. The measured light output from the lamp is 34,530 lumens in- :dic'ating an efliciency of 27.4 lumens per watt as regards the lampand neglecting circuit losses. 4

Fig. 4 illustrates schematically a modification of the present circuit for operation on the ordinary 120 volt, 60 cycle A.C. supply generally available. Like reference numerals in this figure denote corresponding parts with reference to the circuit of Fig. 1. For ease of illustration all the circuit elements have been symbolically illustrated.

Both the main current regulating loop and the auxiliary starting loop are energized from terminals T T adapted to be connected to the usual 120 volt, 60 cycle A.C. supply. The auxiliary starting loop is the same as has been illustrated in Fig. l and is energized upon the closure of switch S through normally closed switch S The main discharge current regulating loop has been modified by the provision of an autotransformer 26 comprising a primary winding 27 and a high-reactance secondary winding 28 connected in series therewith across capacitor C The primary winding forms the input circuit of the transformer whereas the primary and secondary windings in series form the output circuit. The output circuit provides the necessary voltage for operating the lamp and at the same time the leakage reactance of secondary winding 28 serves the function of reactor L previously described with respect to Fig. 1. If desired, switch S may be a time delay relay which opens at a predetermined interval of time after energization of the circuit in order to disable the auxiliary starting loop after the lamp has started.

If desired one or more peaking stages each including a charging capacitor and a saturable inductor may be cascaded in either the main current regulating loop, as described in the copending Wiley application, or in the auxiliary starting loop, in order to achieve the desired steepness and intensity of pulse. In such case, the inductors and capacitors intervening between the input terminals and the final peaking stage together perform the current limiting function of the first inductor, that is L in the auxiliary loop, or L in the main regulating loop.

While the invention has been described in detail by reference to specific constructions embodying its principles, same are intended as illustrative examples and not in order to limit the invention thereto. The appended claims are intended to cover such modifications as will occur to those skilled in the art and coming Within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An operating circuit for an arc lamp comprising a pair of input terminals adapted to be connected to an alternating current source, a main discharge current regulating loop including a first capacitor and a first inductor connected inseries across said input terminals, a pair of output terminals adapted for connection to an arc lamp for pulse energization thereof, a first saturable inductor connected across said first capacitor in series with said output terminals, another pair of input terminals adapted to be connected to an alternating current source, an auxiliary starting loop including a second capacitor and a second inductor connected in series across said other input terminals,'and a second saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic and a coupling winding on said first saturable inductor con nected in series across said second capacitor to generate high-voltage pulses in said first saturable inductor for ionizing said lamp at starting.

2. An operating circuit for an arc lamp comprising a pair of input terminals adapted to be connected to an alternating current source, a main discharge current regulating loop including a first capacitor and a first current limiting inductor connected in series across said input terminals, a pair of output terminals adapted for connection to an arc lamp for pulse energization thereof with a residual current flow for maintaining ionization therein between pulses, a first saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic connected across said first capacitor in series with said output terminals, another pair of input terminals adapted to be connected to an alternating current source, an auxiliary starting loop including a second capacitor and a second current limiting inductor connected in series across said other input terminals, and a second saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic and a coupling winding on said first saturable inductor connected in series across said second capacitor to generate high-voltage pulses in said first saturable inductor for ionizing said lamp at starting.

3. An operating circuit for an arc lamp comprising a pair of input terminals adapted to be connected to an alternating current source, a main discharge current regulating loop including a first capacitor and a substantially linear first inductor connected in series across said input terminals, a pair" of output terminals adapted for connection to an 'arc lamp for puse energization thereof with a residual current flow for maintaining ionization therein between pulses, a first saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic connected across said first capacitor in series with said output terminals, another pair of input terminals adapted to be connected to an alternating current source, an auxiliary starting loop including a second capacitor and a substantially linear second inductor connected in series across said other input terminals, and a second saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic and a coupling winding on the core of said first saturable inductor connected in series across said second capacitor, said first saturable inductor having a relatively high current ratio relative to said coupling winding whereby to generate high-voltage pulses in said first saturable inductor for ionizing said lamp at starting and thereafter permit relatively high current and low voltage pulse energization thereof by said main regulating loop.

4. An operating circuit for an arc lamp comprising a main discharge current regulating loop including a transformer having an input circuit for connection to an alternating voltage source and an output circuit including a high reactance secondary winding, a first capacitor connected across said output circuit, a pair of output terminals adapted for connection to an arc lamp for pulse energization thereof with a residual current flow for maintaining ionization therein between pulses, a first saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic connected across said first capacitor. in series with said output terminals, another: pair of input terminals adapted to be connected to said alternating voltage source, an auxiliary starting: loop including a second; capacitor and a current. limiting inductor connected in; series. across said other input terminals, and asecond saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic and a coupling winding on said first saturable inductor connected in series across said second capacitor to generate high volt age pulses in saidfirst saturabl'e inductor for ionizing said lamp at starting.

5. The combination of an arc lamp comprising: an elongated envelope containing aninert gas at a low pressure and having a pair of self-heating thermionic electrodes sealed into opposite ends, with anoperating circuit comprising input terminals adapted to be connected to an alternating current source, a main discharge current regulating loop including a first capacitor and a first current limiting inductor connected in series across said input terminals, a first saturable inductor having a high permeability core with a substantially rectangular hysteresis loop characteristic connected across said first capacitor in series with said lampfor pulse energizat-ion thereof with a residual currentflow for maintaining ionization therein b twee Pul es ano he P i n u terminals apte t b 0m ts1 Q2 2 lte n in (9 1 e. sourc an aux lia y tartin 09 ncl din a c d capacitor and a second current limiting inductor con nected in series across said other input terminals, and a second saturable inductor having a high permeability core wit a ubstan a y r c n u a hy es s p characteristic and a coupling winding on the core of said fi s at-a ab euducte; cqtm s ccl in se e o s Said second capacitor, sai first saturable inductor having a rela it y' hi h cur en at o el o sa d m p Wind ng wher by t nctate i h-vol a Pu s s n S i fit t sa u l nd c or fo ionizi g d am at Starting a d, he eafte permi la vely h en d w o e pu e ne zet n the wf b s i main eg l r: s 1091 References Cited in the file of this patent UNITED. STATES PATENTS 2,372,857 Setchell Apr. 3, 1945 2,462,371 Engle Feb. 22, 1949 2,653,240 Strange July 6, 1954 2,774,917 Passmore Dec. 18, 1956 

